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Microbes carve tiny rock homes for their barnacle chefs

7 December 2016

By Alice Klein

IT’S as if the rock is crying. Sandstone blocks near Lakes Entrance on the coast of Victoria, south-east Australia, are covered with barnacles that look like they are spilling tears. It now seems that these “tears of the Virgin”, as they are known locally, result from the first known mutualism between these crustaceans and cyanobacteria.

“It is important because it shows how organisms slowly modify their environment – even if the environment seems ‘as solid as rock’,” says John Buckeridge at RMIT University in Melbourne, Victoria. “What is cute here is the relationship between the barnacle and the cyanobacteria that allows this to happen.”

Buckeridge surveyed the site, where barnacles sit higher out of the water than they normally do, and analysed samples in the lab. Working with William Newman from the Scripps Institution of Oceanography in San Diego, California, he found that the barnacles are surrounded by dark-coloured cyanobacteria, which feed on the crustaceans’ nitrogen-rich waste. This results in a rounded eye shape, with the barnacle looking like the iris and pupil at the centre, from which the tears appear to fall.

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“These associations between microbes and their hosts form a coherent biological entity”

“These associations between microbes and their hosts form a coherent biological entity, or ‘holobiont’,” says Ezequiel Marzinelli at the University of New South Wales, Australia. “These components must be studied together if we are to have an understanding of biological systems.”

This article appeared in print under the headline “Microbes make barnacles weep solidifying tears”